1. Field of the Invention
The present invention relates generally to the design and manufacture of disk drive head suspensions. In particular, the present invention is a method for balancing the mass of suspensions to optimize resonance performance, and suspensions having mass balancing structures.
2. Description of the Related Art
Head gimbal assemblies (HGAs), also sometimes known as head suspension assemblies (HSAs), are commonly used in rigid magnetic disk drives to support magnetic heads in close proximity to the rotating disk surfaces. Suspension assemblies of this type typically include an air bearing head slider assembly mounted to a suspension. The suspension includes a load beam having a mounting region on its proximal end and a gimbal or flexure on its distal end. When incorporated into a disk drive the mounting region is mounted to an actuator or positioning arm which supports the suspension assembly over the rotating disk. A baseplate is typically welded to the mounting region to increase the rigidity of the mounting region and to provide a mechanism for securely mounting the suspension assembly to the positioning arm. The load beam is an elongated and often generally triangularly-shaped member which includes a spring region adjacent to the mounting region, and a rigid region which extends from the spring region. The flexure can be manufactured as a separate member and welded to the distal end of the load beam, or formed as an integral member in the distal end of the load beam. The air bearing head slider assembly contains a magnetic head and is typically bonded to the flexure by adhesive. The flexure allows the head slider assembly to move or xe2x80x9cgimbalxe2x80x9d(about rotational pitch and roll axes) with respect to the distal end of the load beam and thereby follow variations in the surface of the spinning disk. To enable the pivotal flexure movement, the surface of the flexure to which the head slider assembly is bonded is typically spaced from the adjacent surface of the load beam by structures known as load point dimples or formed offsets.
Suspensions are commonly manufactured by chemically etching flat or unformed load beam blanks from thin sheets of stainless steel. Flat and unformed flexure blanks are etched in a similar manner from sheets of stainless steel. During subsequent manufacturing operations side rails, load point dimples and any other structures which extend upwardly or downwardly from the web or generally planar surface of the load beam are formed on the load beam blanks by mechanical bending procedures. Any dimples, offsets or other structures on the flexures requiring deformation of this type are formed in a similar manner. After forming, the flexures are welded to the distal end of the load beams. Baseplates are also welded to the suspensions following the forming operations.
The product of these etching, welding and forming operations are generally flat suspensions (i.e., the mounting region, spring region and rigid region of the load beam are generally coplanar and at the same height. During subsequent manufacturing operations the spring region of the load beam is rolled around a curved mandrel or otherwise bent in such a manner as to plastically bend or permanently deform the spring region. The rolling operation imparts a curved shape to the spring region and causes the flexure to be offset from the mounting region when the suspension is in its unloaded or free state.
As noted above, the suspension supports the slider assembly over the magnetic disk. In reaction to the air pressure at the surface of the spinning disk, the slider assembly develops an aerodynamic force which causes the slider assembly to lift away from and xe2x80x9cflyxe2x80x9d over the disk surface. To counteract this hydrodynamic lifting force, the head suspension assembly is mounted to the disk drive with the suspension in a loaded state so the bent spring region of the suspension forces the head slider assembly toward the magnetic disk. The height at which the slider assembly flies over the disk surface is known as the xe2x80x9cfly height.xe2x80x9d The force exerted by the suspension on the slider assembly when the slider assembly is at fly height is known as the xe2x80x9cgram load.xe2x80x9d
An important performance-related criteria of a suspension is specified in terms of its resonance characteristics. In order for the head slider assembly to be accurately positioned with respect to a desired track on the magnetic disk, the suspension must be capable of precisely translating or transferring the motion of the positioning arm to the slider assembly. An inherent property of moving mechanical systems, however, is their tendency to bend and twist in a number of different modes when driven back and forth at certain rates known as resonant frequencies. Any such bending or twisting of a suspension can cause the position of the head slider assembly to deviate from its intended position with respect to the desired track. Since the head suspension assemblies must be driven at high rates of speed in high performance disk drives, it is desirable for the resonant frequencies of a suspension to be as high as possible. The detrimental effects of the bending and twisting at the resonance frequencies can also be reduced by minimizing the extent of the bending and twisting motion of the suspension (also known as the gain) at the resonant frequencies.
Common bending and twisting modes of suspensions are generally known and discussed, for example, in the Yumura et al. U.S. Pat. No. 5,339,208 and the Hatch et al. U.S. Pat. No. 5,471,734. Modes which result in lateral or transverse motion (also known as off-track motion) of the head slider are particularly detrimental since this motion causes the head slider to move from the desired track on the disk toward an adjacent track. The three primary modes which produce this transverse motion are known as the sway, first torsion and second torsion modes. The sway mode is a lateral bending mode (i.e., the suspension bends in primarily the transverse direction along its entire length). The first and second torsion modes are twisting modes during which the suspension twists about a rotational axis which extends along the length of the suspension. The first and second torsion modes produce transverse motion of the head slider if the center of rotation of the suspension is not aligned with the gimbal point of the head slider.
Various techniques for compensating for the detrimental effect of resonance modes are known. The Yumura et al. U.S. Pat. No. 5,339,208, for example, states that it is desirable to locate the shear center at the gimbal contact point between the flexure and load beam. The Hatch et al. U.S. Pat. No. 5,471,734 notes that the position, shape and size of the roll or bend in the spring region of the suspension, characteristics sometimes referred to as the radius geometry or radius profile of the suspension, can affect resonance characteristics.
The resonance characteristics of a suspension are also dependent upon the geometry and other characteristics of the rails. In addition to the desired resonance performance, rail design factors include the ability of the suspension to accommodate lead wires extending from the read/write head and volume or size constraints. The rails cannot, therefore, always be designed solely for optimized resonance characteristics.
Integrated lead suspensions have conductive traces which are bonded to and extend along the length of the load beams. The integrated leads can be damaged if bent, and therefore limit the extent to which suspensions of these types can be formed for resonance optimization.
Although suspensions are commonly manufactured from stainless steel which can be formed, other materials such as ceramics, cermets and less formable metals can also be used. Suspensions manufactured from materials of these types are not readily susceptible to conventional forming processes for adjustment of their resonance characteristics.
It is evident that there is a continuing need for suspensions having improved resonance characteristics. In particular, there is a need for methods for adjusting the resonance characteristics of suspensions that do not include forming. Suspensions which can have their resonance characteristics adjusted without the need for load beam forming are also needed. Suspensions and associated adjusting methods which enable the optimization for several resonance characteristics would be particularly advantageous.
The present invention includes a disk drive suspension capable of being adjusted to improve resonance characteristics and a method of making such adjustments. In particular, the present invention includes a disk drive suspension having a load beam with a distal end, an actuator arm mounting region on a proximal end, and a rigid region. A spring region is between the rigid region and the actuator arm mounting region. A head mounting region is on a distal end of the load beam and is for receiving a transducer head. The disk drive suspension also includes one or more mass balancing structures located on the load beam between the actuator arm mounting region and the head mounting region. The mass balancing structures are adapted for permanent displacement or removal from the load beam to adjust the mass distribution of the load beam.
A method of adjusting resonance characteristics of the disk drive suspension includes determining an adjust location on the load beam at which a resonance characteristic to be adjusted is sensitive to changes in mass. The mass distribution of the load beam is adjusted at the adjust location.
The resonance characteristics of the disk drive suspension of the present invention advantageously can be efficiently optimized at any stage in the manufacture of the suspension, including after the suspension has been incorporated into a head stack assembly. Additionally, the disk drive suspension and method for adjustment thereof advantageously provide for adjustment of several resonance characteristics.